A liquid crystal display device is composed of a liquid crystal panel as a display panel and a backlight as an external light source placed in the rear surface side of the liquid crystal panel. Among these, the backlight comprises a plurality of cold cathode fluorescent lamps as a linear light source and an optical member for converting a linear light emitted from each cold cathode fluorescent lamp into a surface light. The optical member is constituted normally by laminating multiple of such as a diffuser plate, a diffuser sheet, a lens sheet, and a brightness enhancing sheet, however, with such configuration, the emitted light is diffused easily in a direction not used for display, resulting in undesirable light use efficiency.
Considering the foregoing, the invention disclosed in Patent Literature 1 has been known as an example of the optical member having improved light use efficiency. In the above invention, a lens portion having a plurality of unit lenses arrayed therein is provided on the front surface, whereas a reflecting layer having an opening is provided on the back surface. The reflecting layer is placed in the area corresponding to the part where lights of the unit lenses are not converged, whereas the opening is placed in the area corresponding to the light converging part of the unit lenses, and therefore, the light diffusing angle can be easily controlled by adjusting the size ratio between the reflecting layer and the opening. Consequently, the emitted light in the direction not used for display can be reduced, and thereby improving the light use efficiency.    [Patent Literature 1]: Japanese Unexamined Patent Publication No. 2005-221619